1. Field of the Invention
The present invention relates to aerosol medication delivery systems. More particularly, the invention concerns an improved aerosol inhalation apparatus that is very useful for dispensing pharmaceuticals in the treatment of respiratory or pulmonary diseases and for systemic delivery of drugs via aerosolization.
2. Discussion of the Prior Art
Therapeutic aerosols are commonly administered to patients suffering from numerous types of pulmonary diseases. Specific medications, include beta.sub.2 agonists, anticholinergies, cromolyn sodium, and steroids. More recently the aerosol method of delivery has been used to administer Pentamidine to patients afflicted with AIDS, and is presently under consideration as a delivery means for insulin in the treatment for diabetes. Experience has shown that the use of aerosols to treat lung disease is highly advantageous in that it produces optimal therapy with minimum side effects. Both physical and clinical factors affect aerosol deposition in the lungs. Physical factors include inertial impaction, sedimentation, and diffusion. Clinical factors include particle size, ventilatory pattern and lung function. Aerosols larger than 5 micron aerodynamic diameter (AD) poorly penetrate the upper respiratory tract. Those in the 0.2 to 2 micron range tend to have their maximum disposition in the lung parenchyma.
In general the devices used for producing medical aerosols fall into three categories; the small volume nebulizer (SVN), the metered dose inhaler (MDI), and the powder dose inhaler (PDI). Although the small volume nebulizer (SVN) has traditionally been the apparatus of choice for delivery of therapeutic aerosols, many institutions are now switching to the MDI. The small volume nebulizer (SVN) apparatus typically consists of disposable or reusable nebulizer, a mouthpiece or facemask, and a pressurized gas source usually oxygen or air. The metered dose inhaler (MDI), on the other hand, typically contains the active drug, a metering valve, and chlorofluorcarbon (CFC) propellants. The drug containing canister of the device is generally fitted to a mouthpiece actuator, and activation by compression of the canister into the mouthpiece results in the release of a unit dose of medication.
There is extensive literature indicating the successes of aerosol therapies, as well as the difficulties of using the aerosols properly. See, for example, Respiratory Infection: Diagnosis and Management. J. E. Pennington ed. Raven Press, New York chest 1981, 80:911-915: Arch, Int. Med. 1973, 131:88-91. Notwithstanding the very considerable development of aerosols and methods of using the same, there is still room for improvement in the administration of pharmaceutical aerosols.
A major problem of aerosol therapy is to deposit the aerosol on the walls of small bronchi and bronchioles, where the action of the medication is most often required. Less than 10% of the medication delivered by standard multi-dose inhalers reaches the typical patient's lungs. Most of the 90% of the medication which does not penetrate the target area is deposited in the mouth, throat, and trachea, and is eventually ingested. A small fraction of the aerosol is exhaled.
For effective utilization, the aerosol should consist of small particles, less than 5 microns AD, since larger particles cannot negotiate the sharp turns to the lung and are deposited in the orophapynx due to inertial effects. In order to minimize mouth deposition further it has been shown that the volumetric flow rate of the inhaled aerosol should be below 30 liters per minute. Meter dose inhalers deliver aerosol at a high initial velocity directly into the patient's mouth. This high initial velocity of the aerosol is a major factor in the ineffectiveness of many inhaler systems.
Another serious problem inherent in MDI aerosol medication is patient timing coordination. If patient inhalation does not occur on a timely basis with MDI canister actuation, a large percentage of the medication is lost.
Several pharmaceutical manufacturers have included, or sold separately with their MDI aerosol products, what are referred to variously as "spacers" "oral adapters" "space-inhalers" and "spray inhalers" to be used in conjunction with their products. These offer only a partial solution to the problems which typically occur in MDI aerosol delivery.
The apparatus of the present invention provides a very substantial improvement over all prior art MDI-type devices in that it addresses: (1) volumetric flow rate of medication, (2) elimination of patient coordination problems, (3) particle size and (4) environmental protection considerations.